1. Field of the Invention
The present invention generally relates to the field of intravascular medicine and more specifically refers to the field of angioplasty catheters such as guiding catheters used for the placement of medical devices and radiopaque fluids within the body for treatment of vascular diseases.
2. Description of the Prior Art
The use of intravascular catheters for the treatment of cardiovascular disease is well known in the field of medicine. The need for a greater variety of devices to treat different types of circumstances has grown tremendously as the techniques for the use of such devices has progressed.
Prior art guiding catheters are generally comprised of a shaft which is hollow, defining an inner lumen. The shaft is generally comprised of two tubes congruent to each other with a support member therebetween. A hub is connected to the proximal end of the shaft to provide a means for connecting another device such as a syringe to inject fluids, or for providing a means to direct the device in order to place it within the vessel. A tip of a desired shape is provided at the distal end of the shaft.
An example of the prior art catheters as described above is located in U.S. Pat. No. 3,416,531, issued Dec. 17, 1968, to M. L. Edwards, for CATHETER, which describes a catheter constructed with a reinforcement layer to impart torsional rigidity without impairing the flexibility of the device in bending. U.S. Pat. No. 3,485,234, issued Dec. 23, 1969, to R. C. Stevens, for TUBULAR PRODUCTS AND METHOD OF MAKING SAME, discloses placing the stainless steel braid in between a first and a second plastic extrusion. U.S. Pat. No. 5,254,107, issued Oct. 19, 1993, to P. P. Soltesz, for CATHETER HAVING BRAID REINFORCED TRANSITIONAL TIP, discloses a catheter which is constructed of a first tube, a reinforcement member placed over the first tube, and two different polymer tubes placed over the reinforcement layer to create two sections having different flexibilities. PCT publication No. WO 92/15356, published Sep. 17, 1992, to Nita et al., for CARDIOVASCULAR CATHETER HAVING DISCRETE REGIONS OF VARYING FLEXIBILITY, also teaches a catheter which has varying flexibilities along its length.
In order for the physician to place the catheter at the correct location in the vessel, the physician must apply longitudinal and rotational forces. In order for the catheter to transmit these forces from the proximal end to the distal end, the catheter must be rigid enough to push through the blood vessel, but yet flexible enough to navigate the bends in the blood vessel. The catheter must also be torsionally rigid to transmit the applied torque. To accomplish this balance between longitudinal rigidity, torsional rigidity, and flexibility, there is often a support member added to the shaft. This support wire is often comprised of a metal braid or coil imbedded in the shaft. This support wire is often embedded in the shaft between the two layers of tubing that comprise the shaft.
A guiding catheter is guided through the aorta over the aortic arch and down to the ostium of the vessel which is to be treated. Therefore, it is advantageous to have the proximal section be rigid to transmit the forces applied, but to have the distal end more flexible to allow for better placement of the guide catheter. Having the distal section more flexible also creates a less traumatic section to the blood vessel. The distal end of the catheter is rotated, through the transmission of torque from the proximal end, until the tip of the guiding catheter is in the desired position. With the variations of different bend shapes available on the distal ends of these devices and with variations in patient anatomy, each device may need to be torqued more or less in order to correctly place it.
One problem that has surfaced is that as more flexible distal sections are placed on these catheters, the resistance to guide catheter back-out is reduced. Guide catheter back-out is when the guide dis-engages from its preferred positioning, thereby creating the need for the physician to re-position the guiding catheter. Many different guide catheter curve shapes have been designed to overcome this problem, with each giving different levels of support. However, as the flexibility of the distal most section is reduced, the tendency for back-out again increases.
It is possible to construct a device that is very rigid to obtain the correct amount of back-out support. However, the resulting device would be very traumatic to the patient's arteries due to its rigidity. Similarly, it is possible to construct a very flexible device to limit the trauma the device imparts to the blood vessels. However, the device then becomes too flexible and does not provide any back-out support.
Another problem that is seen in current devices is that devices are constructed such that they are equally flexible in all planes. That feature is not always desired.